Exif read: guard better against out of range offests (#2429)
Exif read: guard better against out of range offests (#2429)

The dataptr() function returns nullptr if the offset is out of proper
range. But the array_to_spec function calling dataptr did not check for
a nullptr return, ended up segfaulting.

This can happen with JPEG files that have certain malformed (we think)
sections of their camera maker notes.
OpenImageIO/oiio,lgritz/oiio,lgritz/oiio,lgritz/oiio,lgritz/oiio,OpenImageIO/oiio,OpenImageIO/oiio,OpenImageIO/oiio